Wireless power feeding system and wireless power feeding method

ABSTRACT

An object is to provide a power feeding system and a power feeding method which are more convenient for a power feeding user at the power receiving end, without causing increases in complexity and size of devices. An object is to provide a power feeding system and a power feeding method which also allow a power feeding provider (a company) which feeds power (at the power transmitting end) to supply power without waste. A power feeding device which wirelessly supplies power to a power receiver detects the position and the resonant frequency of the power receiver by receiving a position and resonant frequency detection signal using a plurality of sub-carriers having different frequencies from the power receiver, and controls the frequency of a power signal to be transmitted to the power receiver on the basis of the information. An efficient power feeding service can be offered by transmitting a power signal to the power receiver at an optimum frequency for high power transmission efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless power feeding system and awireless power feeding method.

2. Description of the Related Art

In recent years, electronic devices using electric power as a drivingpower, as typified by mobile devices such as mobile phones or notebookpersonal computers, are often used while being carried.

In addition, transportation means such as bicycles and automobiles whichuse electric power as a driving power have been developed in terms ofits cleanness and safety in the aspect of environment.

It is difficult to supply power to such electronic devices andtransportation means, which are used outdoors or while in motion,constantly from a commercial power supply distributed to each house,through wires. Therefore, portable electronic devices and transportationmeans incorporate batteries which are charged from a commercial powersupply in advance and operate by being supplied with power from thebatteries.

Thus, the operating time of electronic devices is limited by the amountof power stored in the battery, and a user needs to prepare a sparebattery or to find a commercial power supply, from which the battery canbe recharged, outside the house, in order to use the electronic devicecontinuously for a long time.

Therefore, a contactless power feeding system has been proposed and amore efficient power feeding system in view of a problem with anobstacle and the like has been studied so that the battery can be fedwith power even if there is no commercial power supply (see, e.g.,Patent Document 1).

[Reference]

[Patent Document 1] Japanese Published Patent Application No.2010-119246

SUMMARY OF THE INVENTION

However, a contactless power feeding system has a problem in that it hasdifficulty specifying or managing a power feeding user who receivespower (at the power receiving end), controlling the amount of powersupplied to a power receiver, and the like because it is a contactlesssystem.

The addition of circuits having various functions in order to solve theabove problem may lead to increases in complexity and size of devices ina power feeding system and may also result in an increase inmanufacturing cost.

Therefore, it is an object to provide a power feeding system and a powerfeeding method which are more convenient for a power feeding user at thepower receiving end, without causing increases in complexity and size ofdevices.

It is an object to provide a power feeding system and a power feedingmethod which also allow a power feeding provider (a company) which feedspower (at the power transmitting end) to supply power to a powerreceiver without waste.

It is an object to provide a power feeding system and a power feedingmethod which can offer a power feeding service efficient to both a userand a provider by specifying and managing a power feeding user at thepower receiving end and properly controlling the amount of powersupplied to a power receiver.

In wireless power feeding performed by a power feeding device and apower receiver, the power receiver transmits a position and resonantfrequency detection signal using a plurality of signals having differentfrequencies to the power feeding device, and the power feeding devicedetects a resonant frequency which is specific to the power receiver, onthe basis of the position and resonant frequency detection signalreceived and controls the frequency of a power signal to be transmitted(also referred to as a power signal for power transmission) to the powerreceiver on the basis of the information.

The power feeding device can also identify and manage a power receiverby receiving identification information of the power receiver.

A means of wireless power feeding disclosed in this specification willbe briefly described below. One example of wireless power feeding is apower feeding method using an antenna. With a certain antenna shape, theefficiency of transmission of power fed from a power feeding device to apower receiver depends on the frequency of a power signal to betransmitted, the distance between the power feeding device and the powerreceiver, the resonant frequency specific to the power receiver, or thelike.

Note that in this specification, a distance between a power feedingdevice and a power receiver is the shortest distance between an antennaprovided in the power feeding device and an antenna of the powerreceiver.

If the frequency of a power signal to be transmitted is fixed to a givenvalue f₀, the efficiency of transmission of power fed from the powerfeeding device to the power receiver reaches the maximum value when thedistance between the power feeding device and the power receiver isd_(MAX(0)).

The distance d_(MAX) with which the efficiency of transmission of powerfed from the power feeding device to the power receiver reaches themaximum value varies with the frequency f of the power signal to betransmitted and is specific to the frequency f of each power signal.

Thus, if the distance between the power feeding device and the powerreceiver is fixed to a given value d₀, it is possible to determine thefrequency f_(MAX(0)) of a power signal to be transmitted, at which theefficiency of transmission of power fed from the power feeding device tothe power receiver reaches the maximum value.

In this specification, a resonant frequency is defined as f_(MAX(a)) atwhich power transmission efficiency reaches the maximum value, with adistance d_(a) between the power feeding device and the power receiver.

In a wireless power feeding method disclosed in this specification, apower receiver transmits a plurality of signals having differentfrequencies to a power feeding device.

In this specification, a signal having a reference frequency is definedas a base carrier f_(b), and a signal f_(s) which is generated by adivider circuit and a switch on the basis of the base carrier f_(b) andhas a frequency with a lower intensity than that of the base carrier(for example, f_(b)−(f_(b)/16), f_(b)−(f_(b)/32), or the like) isdefined as a sub-carrier f_(s).

In order to generate a plurality of signals having different frequenciesby adjusting the base carrier itself to a base carrier having adifferent frequency, a circuit for adjusting a frequency by adjusting avoltage, such as a power supply circuit, is needed. The addition of sucha circuit may lead to increases in complexity and size of devices in apower feeding system and may also result in an increase in manufacturingcost.

In a wireless power feeding method disclosed in this specification, as aplurality of signals having different frequencies which is to betransmitted from a power receiver, a plurality of sub-carriers f_(s)generated on the basis of a base carrier f_(b) is used. The sub-carriersf_(s) can be adjusted relative to the base carrier f_(b) by a switchprovided between a mixer and a divider circuit.

By providing a switch between a mixer and a divider circuit toeffectively use a plurality of different sub-carriers, there is no needto additionally provide a circuit for adjusting a frequency by adjustinga voltage, such as a power supply circuit, and it is therefore possibleto suppress increases in complexity and size of devices and anaccompanying increase in manufacturing cost.

The power feeding device receives the plurality of signals havingdifferent frequencies which are transmitted from the power receiver.Then, the power feeding device detects the intensities of the pluralityof received signals having different frequencies and determines afrequency of a high intensity signal.

Here, a frequency of a high intensity signal can be referred to as afrequency corresponding to a signal of large voltage amplitude. In otherwords, a frequency of the highest intensity signal can be referred to asa frequency corresponding to a signal of the largest voltage amplitude,and the frequency of the highest intensity signal is a resonantfrequency.

Note that the power feeding device determines the intensities of theplurality of received signals having different frequencies and, inaddition, can find out the position of the power receiver from thefrequencies and intensities. The position of the power receiver can alsobe referred to as the distance between the power feeding device and thepower receiver.

After finding out the resonant frequency, the power feeding devicetransmits a power signal at that resonant frequency to the powerreceiver.

Thus, the power feeding device can supply power to the power receiverwithout waste by transmitting a power signal to the power receiver at anoptimum frequency for high power transmission efficiency.

A configuration for wireless power feeding disclosed in thisspecification will be briefly described below. The power receiver andthe power feeding device each have a transmission/reception circuitportion which transmits and receives electromagnetic waves to and fromthe other and a signal processing circuit portion which processeselectrical signals of the electromagnetic waves to be transmitted andreceived. The signal processing circuit portion of the power receiverhas a power reception control function to control power to be receivedfrom the power feeding device. The signal processing circuit portion ofthe power feeding device has a position and resonant frequency detectionfunction to find out the distance between the power feeding device andthe power receiver and the resonant frequency, and a power transmissioncontrol function to control power to be transmitted to the powerreceiver.

The power receiver includes a power receiving device portion and a powerload portion and can operate the power load portion using power storedin a power storage portion of the power receiving device portion. Inthis specification, a power receiver means an object which operatesusing received power as driving power, and examples of the powerreceiver include portable electronic devices such as mobile phones,transportation means driven by an electric motor (automobiles, motorizedbicycles, aircrafts, ships, and railroad cars), and the like.

One embodiment of a power feeding system disclosed in this specificationincludes a power feeding device and a power receiver including a powerreceiving device portion. The power feeding device includes atransmission/reception circuit portion which transmits and receives anelectromagnetic wave, a signal processing circuit portion whichprocesses an electrical signal of the electromagnetic wave to betransmitted and received by the transmission/reception circuit portion,and a power supply portion which supplies power to be transmitted to thepower receiver. The signal processing circuit portion of the powerfeeding device has a position and resonant frequency detection functionto detect the position and the resonant frequency of the power receiver,and a power transmission control function to control power to betransmitted to the power receiver. The power receiving device portion ofthe power receiver includes a transmission/reception circuit portionwhich transmits and receives an electromagnetic wave, a signalprocessing circuit portion which processes an electrical signal of theelectromagnetic wave to be transmitted and received by thetransmission/reception circuit portion, and a power storage portionincluding a secondary battery which stores power transmitted from thepower feeding device and supplies power to be consumed by a power loadportion. The transmission/reception circuit portion of the powerreceiving device portion includes an antenna circuit, a rectifiercircuit, a mixer, a demodulation circuit, an oscillator circuit, adivider circuit, and a switch. The switch is provided between the mixerand the divider circuit. The signal processing circuit portion of thepower receiving device portion has a power reception control function tocontrol power to be received from the power feeding device.

Another embodiment of a power feeding system disclosed in thisspecification includes a power feeding device and a power receiverincluding a power receiving device portion. The power feeding deviceincludes a transmission/reception circuit portion which transmits andreceives an electromagnetic wave, a signal processing circuit portionwhich processes an electrical signal of the electromagnetic wave to betransmitted and received by the transmission/reception circuit portion,and a power supply portion which supplies power to be transmitted to thepower receiver. The signal processing circuit portion of the powerfeeding device has a position and resonant frequency detection functionto detect the position and the resonant frequency of the power receiver,and a power transmission control function to control power to betransmitted to the power receiver. The power receiving device portion ofthe power receiver includes a transmission/reception circuit portionwhich transmits and receives an electromagnetic wave, a signalprocessing circuit portion which processes an electrical signal of theelectromagnetic wave to be transmitted and received by thetransmission/reception circuit portion, a power storage portionincluding a secondary battery which stores power transmitted from thepower feeding device and supplies power to be consumed by a power loadportion, and a detection portion which detects the voltage, the current,or the voltage and current outputted from the secondary battery. Thetransmission/reception circuit portion of the power receiving deviceportion includes an antenna circuit, a rectifier circuit, a mixer, ademodulation circuit, an oscillator circuit, a divider circuit, and aswitch. The switch is provided between the mixer and the dividercircuit. The signal processing circuit portion of the power receivingdevice portion has a power reception control function to control powerto be received from the power feeding device.

In each of the above embodiments, the transmission/reception circuitportion of the power receiving device portion can include an antennacircuit, a rectifier circuit, a modulation circuit, a demodulationcircuit, an oscillator circuit, and a power supply circuit.

In each of the above embodiments, the power receiver may include amemory portion which stores identification information to be read by thesignal processing circuit portion of the power receiving device portion,and the signal processing circuit portion of the power feeding devicemay have an identification function to identify the identificationinformation.

One embodiment of a power feeding method disclosed in this specificationincludes a first step of transmitting a position and resonant frequencydetection signal using a plurality of sub-carriers having differentfrequencies from a power receiver to a power feeding device, anddetecting the position and the resonant frequency of the power receiverby the power feeding device, a second step of adjusting the frequency ofa power signal to be transmitted from the power feeding device on thebasis of the position and the resonant frequency of the power receiverand transmitting power from the power feeding device to the powerreceiver, and a third step of storing the power transmitted from thepower feeding device in a secondary battery of a power storage portionof the power receiver.

The power receiver can transmit a plurality of signals having differentfrequencies as a position and resonant frequency detection signal, andthe power feeding device can detect the position and the resonantfrequency of the power receiver by receiving the plurality of signalshaving different frequencies and detecting the intensities of theplurality of signals having different frequencies.

The power receiver may detect the voltage, the current, or the voltageand current outputted from the secondary battery and transmit a powerfeeding request signal or a power reception end signal to the powerfeeding device according to the detection information.

In the above embodiment, a step of recognizing identificationinformation of the power receiver with the power feeding device may beperformed before the first step of detecting the position and theresonant frequency of the power receiver.

In power feeding performed by the power feeding device and the powerreceiver, a power signal is transmitted to the power receiver at anoptimum frequency for high power transmission efficiency on the basis ofthe position and the resonant frequency information of the powerreceiver; accordingly, power can be supplied to the power receiverwithout waste.

Therefore, it is possible to provide a power feeding system and a powerfeeding method which are more convenient for a power feeding user,without causing increases in complexity and size of devices.

It is possible to provide a power feeding system and a power feedingmethod which also allow a power feeding provider (a company) which feedspower (at the power transmitting end) to supply power to a powerreceiver without waste.

It is possible to provide a power feeding system and a power feedingmethod which can offer a power feeding service efficient to both a userand a provider by specifying and managing a power feeding user at thepower receiving end and properly controlling the amount of powersupplied to a power receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 2 illustrates the relationship between the frequency and theintensity of an electrical signal.

FIG. 3 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 4 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 5 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 6 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 7 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIGS. 8A and 8B each illustrate an embodiment of a wireless powerfeeding system and a wireless power feeding method.

FIG. 9 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 10 illustrates an embodiment of a power receiver.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the drawings. Note that the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that modes and details disclosed herein can bemodified in various ways. In addition, the present invention should notbe construed as being limited to the description in the embodimentsgiven below.

Note that ordinal numbers such as “first”, “second”, and “third” areused for convenience and do not denote the order of steps or thestacking order of layers. In addition, the ordinal numbers in thisspecification do not denote any particular names to define theinvention.

Embodiment 1

In this embodiment, an embodiment of a wireless power feeding system anda wireless power feeding method is described with reference to FIGS. 1to 4.

FIG. 1 illustrates components of a power feeding device and a powerreceiver included in the wireless power feeding system of thisembodiment, in independent blocks which are classified according totheir functions. However, there is not necessarily a one-to-onecorrespondence between components and functions, and the power feedingsystem may operate using a plurality of components and a plurality offunctions in conjunction with each other.

In the wireless power feeding system in FIG. 1, a power feeding device20 and a power receiver 10 transmit and receive signals to and from eachother wirelessly (by an electromagnetic wave), and power is suppliedfrom the power feeding device 20 to the power receiver 10 withoutcontact.

The power feeding device 20 includes a transmission/reception circuitportion 210 which transmits and receives electromagnetic waves, a signalprocessing circuit portion 220 which processes electrical signals of theelectromagnetic waves to be transmitted and received, and a power supplyportion 230 which supplies power to be transmitted to the power receiver10.

The transmission/reception circuit portion 210 includes an antennacircuit 211, a rectifier circuit 212, a modulation circuit 213, ademodulation circuit 214, an oscillator circuit 215, and a power supplycircuit 216.

An electromagnetic wave (a signal) received by the antenna circuit 211is converted into an electrical signal by the antenna circuit 211 andrectified in the rectifier circuit 212. The rectified signal isdemodulated in the demodulation circuit 214 and then transmitted to thesignal processing circuit portion 220. On the other hand, a transmissionsignal generated in the signal processing circuit portion 220 istransmitted from the antenna circuit 211 to the power receiver 10 as anelectromagnetic wave (a signal) when voltage is applied to the antennacircuit 211 by the modulation circuit 213 in response to a signal with acertain frequency generated in the power supply circuit 216 and theoscillator circuit 215. Note that the frequency of a signal transmittedfrom the oscillator circuit 215 is adjusted by the power supply circuit216.

In the case where the transmission signal is a power signal for powertransmission, the signal processing circuit portion 220 receives powerfrom the power supply portion 230. The power supply portion 230 isconnected to a power supply network or a power generation system inorder to supply power to the power receiver 10.

The power receiver 10 includes a power receiving device portion 100 anda power load portion 150. The power receiving device portion 100includes a transmission/reception circuit portion 110 which transmitsand receives electromagnetic waves, a signal processing circuit portion120 which processes electrical signals of the electromagnetic waves tobe transmitted and received, a memory portion 140, and a power storageportion 130 including a secondary battery 131 which stores powertransmitted from the power feeding device 20.

The transmission/reception circuit portion 110 includes an antennacircuit 111, a rectifier circuit 112, a mixer 113, a demodulationcircuit 114, an oscillator circuit 115, a divider circuit 118, and aswitch 119.

An electromagnetic wave (a signal) received by the antenna circuit 111is converted into an electrical signal by the antenna circuit 111 andrectified in the rectifier circuit 112. The rectified signal isdemodulated in the demodulation circuit 114 and then transmitted to thesignal processing circuit portion 120. On the other hand, the oscillatorcircuit 115 operates in response to a transmission signal generated inthe signal processing circuit portion 120. Then, a signal (a basecarrier) generated in the oscillator circuit 115 is input to the dividercircuit 118 and the mixer 113. The divider circuit 118 divides thefrequency of the signal generated in the oscillator circuit 115, therebygenerating signals having a plurality of frequencies which are lowerthan the frequency of the signal generated in the oscillator circuit115. The switch 119 is controlled with a signal generated in the signalprocessing circuit portion 120. Then, one of the signals having theplurality of frequencies generated by the divider circuit 118 isselected by the switch 119 and transmitted to the mixer 113. The mixer113 mixes the signal generated in the oscillator circuit 115 with thesignal selected by the switch 119 from the signals generated by thedivider circuit 118. The mixed signal (sub-carrier) is transmitted fromthe antenna circuit 111 to the power feeding device 20.

In response to the signal generated in the signal processing circuitportion 120, the switch 119 is selected plural times, and signals havinga plurality of frequencies corresponding to the number of times theswitch 119 is selected are transmitted to the mixer 113 and mixed withthe signal generated in the oscillator circuit 115. Thus, a plurality ofsub-carriers is transmitted from the antenna circuit 111 to the powerfeeding device 20.

Note that the divider circuit 118 is configured with plural stages ofconnected flip-flop circuits, latch circuits, or the like. The signalshaving the plurality of frequencies generated by the divider circuit 118are determined by the number of stages of flip-flop circuits, latchcircuits, or the like. For example, when the divider circuit 118 isconfigured with three stages of flip-flop circuits, latch circuits, orthe like, three kinds of signals having a plurality of frequencies canbe generated by the divider circuit 118.

In the case where the received electromagnetic wave is anelectromagnetic wave for power reception, it is converted into anelectrical signal by the antenna circuit 111, rectified in the rectifiercircuit 112, and then stored as power (electrical energy) in thesecondary battery 131 of the power storage portion 130 via the signalprocessing circuit portion 120.

The secondary battery 131 is a power storage means. For example, alead-acid battery, a nickel-cadmium battery, a nickel-hydride battery, alithium-ion battery, or the like can be used.

Note that in the block diagrams in FIG. 1, a DC-DC converter can beprovided as appropriate. In addition, in the power storage portion 130,a power supply circuit or an overcharge control circuit for controllingoperation of the power supply circuit so as to prevent overcharging ofthe secondary battery 131 may be provided as appropriate, and the powersupply circuit can supply power (electrical energy) stored in thesecondary battery 131 to the power load portion 150 as a constantvoltage.

The power storage portion 130 may include a discharge control circuit.The discharge control circuit has a function to control the supply ofpower or the amount of power to be supplied to the power load portion150. The discharge control circuit makes it possible to supply power asneeded or adjust the amount of power to be supplied.

Although not illustrated in FIG. 1 (and FIG. 6), the power receivingdevice portion 100 includes a power supply circuit and a capacitor forgenerating power to be supplied to the power receiving device portion100. In the transmission/reception circuit portion 110, power isgenerated from the signal received by the antenna circuit 111. Therectifier circuit is used for the generation of power. The generatedpower is supplied to the transmission/reception circuit portion 110, thesignal processing circuit portion 120, and the memory portion 140. Notethat in the case where power is stored in the secondary battery 131 ofthe power storage portion 130, power may be supplied from the secondarybattery 131 to the transmission/reception circuit portion 110, thesignal processing circuit portion 120, the memory portion 140, and thelike. In the case of the configuration where power is supplied from thesecondary battery 131, the power supply circuit and the capacitor forgenerating power to be supplied to the power receiving device portion100 are not necessarily provided.

The signal processing circuit portion 220 of the power feeding device 20has a position and resonant frequency detection function 223 to detectthe distance to the power receiver 10 and the resonant frequency of thepower receiver 10, and a power transmission control function 222 tocontrol power to be transmitted to the power receiver 10.

On the other hand, the signal processing circuit portion 120 of thepower receiver 10 has a power reception control function 122 to controlpower to be received from the power feeding device 20.

The power feeding device 20 which wirelessly supplies power to the powerreceiver 10 detects the position and the resonant frequency of the powerreceiver 10 to be supplied with power and controls the frequency of apower signal to be transmitted to the power receiver 10 on the basis ofthe information.

Note that in this specification, the distance between the power feedingdevice 20 and the power receiver 10 is the shortest distance between anantenna provided in the power feeding device 20 and an antenna of thepower receiver 10. FIG. 4 illustrates an example of power feeding with adistance d between a power receiver antenna 117 provided in the powerreceiver 10 and a power feeding device antenna 217 provided in the powerfeeding device 20. In FIG. 4, the power receiver antenna 117 and thepower feeding device antenna 217 are disposed at a distance d from eachother, and power feeding is performed by generating a magnetic field300. FIG. 4 illustrates an example of power feeding by anelectromagnetic induction method using coil antennas as the antennas,and illustrates one embodiment of the shape of antennas and the methodfor transmitting electromagnetic waves which can be employed in theinvention disclosed in this specification.

In this specification, there is no particular limitation on thefrequency of a power feeding electromagnetic wave and the frequency maybe in any frequency band as long as power can be transmitted. Forexample, the frequency of a power feeding electromagnetic wave may be inany of an LF band of 135 kHz (long wave), an HF band of 13.56 MHz, a UHFband of 900 MHz to 1 GHz, and a microwave band of 2.45 GHz.

In this specification, the frequency of electromagnetic waves used as avariety of signals (such as an electrical signal transmittingidentification information and the like and a position and resonantfrequency detection signal) may be in the same frequency band as a powerfeeding electromagnetic wave or may be in a different frequency band.Note that in the case of using frequencies in different frequency bands,separate antennas for the frequencies are preferably provided.

In this specification, the method of transmitting electromagnetic wavesmay be appropriately selected from a variety of methods such as anelectric field coupling method, an electromagnetic induction method, aresonance method, and a microwave method. In order to prevent energyloss due to foreign substances containing moisture, such as rain andmud, the electromagnetic induction method or the resonance method usinga low frequency band, specifically, frequencies of a short wave of 3 MHzto 30 MHz, a medium wave of 300 kHz to 3 MHz, a long wave of 30 kHz to300 kHz, or an ultralong wave of 3 kHz to 30 kHz, is preferably used.

One example of wireless power feeding is a power feeding method using anantenna. With a certain antenna shape, the efficiency of transmission ofpower fed from the power feeding device 20 to the power receiver 10depends on the frequency of a power signal to be transmitted, thedistance between the power feeding device 20 and the power receiver 10,the resonant frequency specific to the power receiver 10, or the like.

If the frequency of a power signal to be transmitted is fixed to a givenvalue f₀, the efficiency of transmission of power fed from the powerfeeding device to the power receiver reaches the maximum value when thedistance between the power feeding device and the power receiver isd_(MAX(0)).

The distance d_(MAX) with which the efficiency of transmission of powerfed from the power feeding device to the power receiver reaches themaximum value varies with the frequency f of the power signal to betransmitted and is specific to the frequency f of each power signal.

Therefore, if the distance between the power feeding device 20 and thepower receiver 10 is fixed to a given value d₀, it is possible todetermine the frequency f_(MAX(0)) of a power signal, at which theefficiency of transmission of power fed from the power feeding device 20to the power receiver 10 reaches the maximum value.

As described above, if the distance between the power feeding device 20and the power receiver 10 is fixed to a given value d₀, the frequency(the resonant frequency) at which the power transmission efficiencyreaches the maximum value can be uniquely determined. In a wirelesspower feeding system disclosed in this specification, in order to obtainthe resonant frequency at which the power transmission efficiencyreaches the maximum value, a power receiver transmits a plurality ofsignals having different frequencies to a power feeding device. Afeature is that signals (sub-carriers) having different frequencieswhich are to be transmitted from the power receiver to the power feedingdevice are generated on the basis of a base carrier used for wirelesspower feeding.

Then, the power feeding device 20 receives the plurality of signals(sub-carriers) having different frequencies which is transmitted fromthe power receiver 10. Next, the power feeding device 20 selects asignal having a frequency with the highest intensity (a resonantfrequency) from the plurality of received signals (sub-carriers) havingdifferent frequencies. Furthermore, the power feeding device 20transmits a power transmission signal to the power receiver 10 at theresonant frequency.

In the above manner, power can be supplied to the power receiver withoutwaste by transmitting a power signal to the power receiver at an optimumfrequency (a resonant frequency) for high power transmission efficiency.

Accordingly, the power receiver transmits a plurality of signals havingdifferent frequencies to the power feeding device, as a signal fordetecting the position relative to the power feeding device and theresonant frequency.

A sub-carrier defined in this specification will be described withreference to FIG. 2. A base carrier f_(b) that is a signal generated bythe oscillator circuit 115 and having a reference frequency and signalsgenerated by the divider circuit 118 and having a plurality offrequencies are mixed together using the mixer 113; thus, a plurality ofsub-carriers f_(s−2), f_(s−1), f_(s+1), f_(s+2) . . . is generated. Thefrequencies of the sub-carriers are at regular intervals relative to thefrequency of the base carrier f_(b). In addition, the intensities of thesub-carriers are lower than the intensity of the base carrier.

In order to generate a plurality of signals having different frequenciesby adjusting the base carrier to a base carrier having a differentfrequency, a circuit for adjusting a frequency by adjusting a voltage,such as a power supply circuit, is needed. The addition of such acircuit may lead to increases in complexity and size of devices in apower feeding system and may also result in an increase in manufacturingcost.

In this embodiment, as the plurality of signals having differentfrequencies which is to be transmitted from the power receiver, aplurality of sub-carriers f_(s) generated on the basis of a base carrierf_(b) is used. The sub-carriers f_(s) can be adjusted relative to thebase carrier f_(b) by the switch 119 provided between the mixer 113 andthe divider circuit 118.

By providing the switch 119 between the mixer 113 and the dividercircuit 118 to effectively use a plurality of different sub-carriers,there is no need to additionally provide a circuit for adjusting afrequency by adjusting a voltage, such as a power supply circuit, and itis therefore possible to suppress increases in complexity and size ofdevices and an accompanying increase in manufacturing cost.

An embodiment of a wireless power feeding method is described withreference to a flow chart of FIG. 3. Note that a power feeding device Kcorresponds to the power feeding device 20 in FIG. 1 and a powerreceiver J corresponds to the power receiver 10 in FIG. 1.

First, the power receiver J transmits a position and resonant frequencydetection signal to the power feeding device K (JB1: Transmission ofposition and resonant frequency detection signal). As the position andresonant frequency detection signal, a plurality of signals havingdifferent frequencies can be used. The power feeding device K receivesthe position and resonant frequency detection signal of the powerreceiver J (KB1: Reception of position and resonant frequency defectionsignal), and detects the position and resonant frequency of the powerreceiver J with the intensities and times of the plurality of receivedelectrical signals having different frequencies (KB2: Detection ofposition and resonant frequency) (B: Position and resonant frequencydetection step).

The power feeding device K may store information used for the detection(such as the relationship between transmission efficiency and atransmission distance at a resonant frequency) in a memory portion ofthe power feeding device K in advance. Alternatively, at the time ofdetection, the power feeding device K may communicate with anothermanagement server or the like and perform detection on the basis ofinformation obtained from the server.

The power feeding device K adjusts the frequency of a power signal to betransmitted, on the basis of the detected position and resonantfrequency of the power receiver J, so as to obtain the maximum powertransmission efficiency (KC1: Adjustment of power transmissionfrequency). Power can be supplied to the power receiver without waste bytransmitting a power signal to the power receiver at an optimumfrequency for high power transmission efficiency. As a result, powerfeeding which is efficient and convenient for both the power feedingdevice K and the power receiver J can be performed.

The power feeding device K transmits a power transmission start signalto the power receiver J (KC2: Transmission of power transmission startsignal), and the power receiver J receives the power transmission startsignal (JD1: Reception of power transmission start signal) and transmitsa power reception start signal when it is ready for power reception(JD2: Transmission of power reception start signal). The power feedingdevice K receives the power reception start signal from the powerreceiver J (KC3: Reception of power reception start signal) and startspower transmission (KC4: Start of power transmission). By powertransmission from the power feeding device K, the power receiver Jstarts power reception (JD3: Start of power reception).

The power feeding device K transmits a power transmission end signal tothe power receiver J by using the power transmission control function222 after transmitting a proper amount of power (KC5: Transmission ofpower transmission end signal). The power receiver J receives the powertransmission end signal from the power feeding device K (JD4: Receptionof power transmission end signal), then transmits a power reception endsignal to the power feeding device K (JD5: Transmission of powerreception end signal), and ends the power reception (JD6: End of powerreception) (D: Power reception control step). The power feeding device Kreceives the power reception end signal from the power receiver J (KC6:Reception of power reception end signal) and also ends the powertransmission (KC7: End of power transmission) (C: Power transmissioncontrol step).

Note that the start or end of power transmission from the power feedingdevice K may be at the same time as the transmission of the powertransmission start signal or the transmission of the power transmissionend signal. The start or end of power reception may also be at the sametime as the transmission of the power reception start signal or thetransmission of the power reception end signal. Since the powertransmission and the power reception occur in conjunction with eachother, the power reception by the power receiver J can be started at thesame time as the start of power transmission from the power feedingdevice K, and the power reception by the power receiver J can be endedat the same time as the end of power transmission from the power feedingdevice K. FIG. 3 illustrates an example where the power feeding device Ksignals the end of power feeding to the power receiver J and ends thepower transmission, but the power receiver J can request the end ofpower feeding of the power feeding device K to end the powertransmission from the power feeding device K.

As a result, the power load portion 150 can be operated using powerstored in the secondary battery 131 of the power storage portion 130 ofthe power receiving device portion 100. In this specification, a powerreceiver means an object which operates using received power as adriving power, and examples of the power receiver include portableelectronic devices such as mobile phones, notebook personal computers,cameras such as digital cameras or digital video cameras, digital photoframes, portable game machines, personal digital assistants, andelectronic books, transportation means driven by an electric motor usingpower (automobiles (automatic two-wheeled vehicles, three ormore-wheeled automobiles), motorized bicycles including motor-assistedbicycles, aircrafts, ships, and railroad cars), and the like.

FIG. 10 illustrates a personal digital assistant (PDA) as an example ofthe power receiver. The power receiver 10 in FIG. 10 is a personaldigital assistant including a display panel 51 in a housing 50. In thehousing 50, the power receiving device portion 100 and the power loadportion 150 are provided under the display panel 51. The power receivingdevice portion 100 includes the transmission/reception circuit portion110 which includes the antenna circuit 111, the rectifier circuit 112,the mixer 113, the demodulation circuit 114, the oscillator circuit 115,and the like, the signal processing circuit portion 120, the memoryportion 140, and the power storage portion 130 including the secondarybattery 131. An electromagnetic wave received by thetransmission/reception circuit portion 110 is stored in the secondarybattery 131 of the power storage portion 130 via the signal processingcircuit portion 120. By the supply of power stored in the secondarybattery 131 to the power load portion 150, a semiconductor integratedcircuit and the like provided in the power load portion 150 can bedriven and an image can be displayed on the display panel 51; thus, thepower receiver 10 can be operated as a personal digital assistant.

The power feeding system and the power feeding method in this embodimentenable a user of the power receiver to obtain more convenience andhigher added values, without causing increases in complexity and size ofdevices.

It is also possible to provide a company at the power feeding end with apower feeding system and a power feeding method which can offer avariety of efficient services.

Embodiment 2

In this embodiment, another embodiment of a wireless power feedingsystem and a wireless power feeding method is described with referenceto FIG. 5 and FIG. 6.

FIG. 6 illustrates components of a power feeding device and a powerreceiver included in the wireless power feeding system of thisembodiment, in independent blocks which are classified according totheir functions. FIG. 6 illustrates an example where a detection portion(a voltage/current detection portion 160) which detects the amount ofpower stored in the secondary battery 131 of the power storage portion130 is provided in the wireless power feeding system in FIG. 1 describedin Embodiment 1. The same portions as or portions having functionssimilar to those in Embodiment 1 are similar to those in Embodiment 1and repetitive description will be omitted. In addition, detaileddescription of the same portions is not repeated.

The voltage/current detection portion 160 detects the voltage, thecurrent, or the voltage and current outputted from the secondary battery131 of the power storage portion 130 to find out the amount of powerstored in the secondary battery 131 and transmits the information to thesignal processing circuit portion 120, so that the signal processingcircuit portion 120 controls power reception.

An embodiment of a wireless power feeding method is described withreference to a flow chart of FIG. 5. Note that a power feeding device Kcorresponds to the power feeding device 20 in FIG. 6 and a powerreceiver J corresponds to the power receiver 10 in FIG. 6.

A position and resonant frequency detection step is similar to that inFIG. 3 in Embodiment 1 and is thus not described.

A power transmission control step and a power reception control step aredescribed.

The power feeding device K adjusts the frequency of a power signal to betransmitted, on the basis of the detected position and resonantfrequency of the power receiver J, so as to obtain the maximum powertransmission efficiency (KC1: Adjustment of power transmissionfrequency). Power can be supplied to the power receiver without waste bytransmitting a power signal to the power receiver J at an optimumfrequency for high power transmission efficiency. As a result, powerfeeding which is efficient and convenient for both the power feedingdevice K and the power receiver J can be performed.

The power feeding device K transmits a power transmission start signalto the power receiver J (KC2: Transmission of power transmission startsignal), and the power receiver J receives the power transmission startsignal (JD1: Reception of power transmission start signal) and transmitsa power reception start signal when it is ready for power reception(JD2: Transmission of power reception start signal). The power feedingdevice K receives the power reception start signal from the powerreceiver J (KC3: Reception of power reception start signal) and startspower transmission (KC4: Start of power transmission). By powertransmission from the power feeding device K, the power receiver Jstarts power reception (JD3: Start of power reception).

In this embodiment, an example is described in which information on theamount of power stored in the secondary battery 131, which is detectedby the voltage/current detection portion 160, is also used to controlpower feeding. At the start of power reception by the power receiver J,the voltage/current detection portion 160 detects the voltage, thecurrent, or the voltage and current outputted from the secondary battery131 (JD7: Detection of voltage/current).

The voltage/current detection portion 160 finds out the amount of powerstored in the secondary battery 131 by detecting the voltage, thecurrent, or the voltage and current outputted from the secondary battery131. When the power receiver J determines that the amount of powerexceeds the capacity of the secondary battery 131, it transmits a powerreception end signal to the power feeding device K (JD5: Transmission ofpower reception end signal).

The power feeding device K receives the power reception end signal fromthe power receiver J (KC6: Reception of power reception end signal),then transmits a power transmission end signal to the power receiver J(KC5: Transmission of power transmission end signal), and ends the powertransmission (KC7: End of power transmission). The power receiver Jreceives the power transmission end signal from the power feeding deviceK (JD4: Reception of power transmission end signal) and ends the powerreception (JD6: End of power reception).

In this manner, the power receiver J can request the end of powerfeeding of the power feeding device K to end the power transmission fromthe power feeding device K.

As the plurality of signals having different frequencies which is to betransmitted from the power receiver in order to detect the positionrelative to the power feeding device and the resonant frequency, aplurality of sub-carriers f_(s) generated on the basis of a base carrierf_(b) is used. The sub-carriers f_(s) can be adjusted relative to thebase carrier f_(b) by a switch provided between a mixer and a dividercircuit.

By providing a switch between a mixer and a divider circuit toeffectively use a plurality of different sub-carriers, there is no needto additionally provide a circuit for adjusting a frequency by adjustinga voltage, such as a power supply circuit, and it is therefore possibleto suppress increases in complexity and size of devices and anaccompanying increase in manufacturing cost.

In power feeding performed by the power feeding device and the powerreceiver, a power signal is transmitted to the power receiver at anoptimum frequency for high power transmission efficiency on the basis ofthe position and resonant frequency information of the power receiver;accordingly, power can be supplied to the power receiver without waste.

Furthermore, by finding out the amount of power stored in the secondarybattery, power transmission which is more proper to the user request canbe performed. Thus, it is possible to reduce the waste of power due toexcessive power transmission and the deterioration of the secondarybattery 131 due to the supply of power over the capacity. As a result,power feeding which is efficient and convenient for both the powerfeeding device and the power receiver can be performed.

Accordingly, it is possible to provide a power feeding system and apower feeding method which can offer a power feeding service efficientto both a user and a provider.

This embodiment can be implemented in an appropriate combination withthe configurations described in the other embodiments.

Embodiment 3

In this embodiment, another embodiment of a wireless power feedingsystem and a wireless power feeding method is described with referenceto FIG. 7 and FIGS. 8A and 8B.

In this embodiment, an example is described in which a step ofrecognizing identification information of the power receiver is addedbefore the position and resonant frequency detection step in Embodiment1 or 2. The same portions as or portions having functions similar tothose in Embodiment 1 or 2 are similar to those in Embodiment 1 or 2 andrepetitive description will be omitted. In addition, detaileddescription of the same portions is not repeated.

Identification information can be stored in the memory portion of thepower receiver. In addition, the signal processing circuit portion ofthe power feeding device has an identification function to identify theidentification information.

A wireless power feeding method of this embodiment is described withreference to a flow chart of FIG. 7. Note that a power feeding device Kcorresponds to the power feeding device 20 in FIG. 1 and a powerreceiver J corresponds to the power receiver 10 in FIG. 1.

First, the power receiver J transmits identification information to thepower feeding device K (JA1: Transmission of identificationinformation), and the power feeding device K receives the identificationinformation of the power receiver J (KA1: Reception of identificationinformation). The power feeding device K inquires for and checks thereceived identification information (KA2: Inquiry and check ofidentification information), and identifies the power receiver J (A:Identification information recognition step). The process proceeds tothe next step, and power feeding is performed in a manner similar to thepower feeding method in FIG. 3 or FIG. 5.

The power feeding device K may store information for the identificationin the memory portion of the power feeding device K in advance.Alternatively, at the time of identification, the power feeding device Kmay communicate with another management server or the like and performidentification on the basis of information obtained from the server.Alternatively, communication between the power feeding device K and thepower receiver J may be started from the power feeding device K. Forexample, in the case where the power feeding device K have obtainedidentification information of the power receiver J, communication may bestarted by transmission of a signal for inquiring about identificationinformation to the power receiver J in order to identify (search for)the power receiver J having the identification information.

The power feeding device K can adjust the intensity of a power signal tobe transmitted, on the basis of the identification information of thepower receiver J. For example, by reading and considering the amount ofpower which can be stored in the secondary battery 131 of the powerreceiver J on the basis of the identification information, the intensityand frequency of an electromagnetic wave to be transmitted, the powertransmission time, and the like can be controlled.

Alternatively, as in FIG. 8A, the power receiver J can request the startof power feeding of the power feeding device K to start powertransmission from the power feeding device K. FIG. 8A illustrates theidentification information recognition step. First, the power receiver Jtransmits a signal for requesting power feeding to the power feedingdevice K (JA2: Transmission of power feeding request signal). The powerfeeding device K which is placed in a position where it can receive thepower feeding request signal from the power receiver J receives thepower feeding request signal (KA3: Reception of power feeding requestsignal) and transmits a signal for inquiring about identificationinformation of the power receiver J to the power receiver J in responseto the power feeding request signal (KA4: Transmission of identificationinformation inquiry signal). The power receiver J receives theidentification information inquiry signal from the power feeding deviceK (JA3: Reception of identification information inquiry signal) andtransmits identification information of the power receiver J to thepower feeding device K (JA1: Transmission of identificationinformation). The power feeding device K receives identificationinformation from the power receiver J (KA1: Reception of identificationinformation), inquires for and checks the received identificationinformation (KA2: Inquiry and check of identification information), andidentifies the power receiver J. The process proceeds to the next step,and power feeding is performed in a manner similar to the power feedingmethod in FIG. 3 or FIG. 5.

The transmission of the power feeding request signal from the powerreceiver J may be controlled by a user in consideration of the amount ofpower stored in the secondary battery of the power receiver J.Alternatively, the transmission of the power feeding request signal fromthe power receiver J may be set so as to be automatically performeddepending on the amount of power stored in the secondary battery 131.

For example, as illustrated in FIG. 8B, the voltage/current detectionportion 160 detects the voltage, the current, or the voltage and currentoutputted from the secondary battery 131 (JA4: Detection ofvoltage/current), and when the power receiver J determines that theamount of power stored in the secondary battery 131 is smaller than acertain amount of power, it transmits a power feeding request signal tothe power feeding device K (JA2: Transmission of power feeding requestsignal). The process proceeds to the next step, and power feeding isperformed in a manner similar to the power feeding method in FIG. 8A andFIG. 3 or FIG. 5.

Also in this embodiment, as a plurality of signals having differentfrequencies which is to be transmitted from a power receiver, aplurality of sub-carriers f_(s) generated on the basis of a base carrierf_(b) is used. The sub-carriers f_(s) can be adjusted relative to thebase carrier f_(b) by a switch provided between a mixer and a dividercircuit.

By providing a switch between a mixer and a divider circuit toeffectively use a plurality of different sub-carriers, there is no needto additionally provide a circuit for adjusting a frequency by adjustinga voltage, such as a power supply circuit, and it is therefore possibleto suppress increases in complexity and size of devices and anaccompanying increase in manufacturing cost.

In power feeding performed by the power feeding device and the powerreceiver, a power signal is transmitted to the power receiver at anoptimum frequency for high power transmission efficiency on the basis ofthe position and resonant frequency information of the power receiver;accordingly, power can be supplied to the power receiver without waste.

Furthermore, by finding out the specific information of the powerreceiver J or the amount of power stored in the secondary battery, powertransmission which is adapted to the user request can be performed.Thus, it is possible to reduce the waste of power due to excessive powertransmission and the deterioration of the secondary battery 131 due tothe supply of power over the capacity. As a result, power feeding whichis efficient and convenient for both the power feeding device K and thepower receiver J can be performed.

In addition, it is preferable to take measures for security, such asupdating identification information including specific information likepersonal information for each power feeding, deleting unnecessaryidentification information from a power feeding device after finishing arecognition step for power feeding, or encrypting communication whentransmitting identification information.

It is possible to provide a power feeding system and a power feedingmethod which can offer a power feeding service efficient to both a userand a provider, without causing increases in complexity and size ofdevices.

This embodiment can be implemented in an appropriate combination withthe configurations described in the other embodiments.

Embodiment 4

In this embodiment, another embodiment of a wireless power feedingsystem and a wireless power feeding method is described with referenceto FIG. 9.

The power feeding system and the power feeding method in thisspecification can also be applied to a plurality of power feedingdevices and a plurality of power receivers. In this embodiment, anexample is described in which the power feeding system and the powerfeeding method described in any of Embodiments 1 to 3 are applied to aplurality of power feeding devices and a plurality of power receivers.The same portions as or portions having functions similar to those inany of Embodiments 1 to 3 are similar to those in any of Embodiments 1to 3 and repetitive description will be omitted. In addition, detaileddescription of the same portions is not repeated.

For example, in the case where power is fed from one power feedingdevice to a plurality of power receivers, the position and the resonantfrequency of each of the power receivers can be found, and the frequencyof a power signal to be transmitted can be controlled so as to obtainoptimum power transmission efficiency. FIG. 9 illustrates an examplewhere power is fed to each of power receivers Ja 10 a, Jb 10 b, and Jc10 c.

The power receivers Ja 10 a, Jb 10 b, and Jc 10 c are placed atdifferent distances from a power feeding device K 20 and have specificresonant frequencies.

The power feeding device K 20 feeds power by obtaining the position andresonant frequency information of the power receivers Ja 10 a, Jb 10 b,and Jc 10 c and determining the frequencies f(d(Ja)), f(d(Jb)), andf(d(Jc)) of power signals to be transmitted, on the basis of theinformation, so as to obtain optimum power transmission efficiency foreach of the power receivers.

Also in this embodiment, as a plurality of signals having differentfrequencies which is to be transmitted from a power receiver, aplurality of sub-carriers f_(s) generated on the basis of a base carrierf_(b) is used. The sub-carriers f_(s) can be adjusted relative to thebase carrier f_(b) by a switch provided between a mixer and a dividercircuit.

By providing a switch between a mixer and a divider circuit toeffectively use a plurality of different sub-carriers, there is no needto additionally provide a circuit for adjusting a frequency by adjustinga voltage, such as a power supply circuit, and it is therefore possibleto suppress increases in complexity and size of devices and anaccompanying increase in manufacturing cost.

A power signal is transmitted to each power receiver at an optimumfrequency for high power transmission efficiency on the basis of theposition and resonant frequency information of the power receiver;accordingly, power can be supplied to the power receivers without waste.

Although FIG. 9 illustrates a case where a single power feeding deviceis used, a plurality of power feeding devices may be used. Even with aplurality of power feeding devices, power feeding between the powerfeeding devices and the power receivers can be performed by finding outinformation on the distances and resonant frequencies and optimizing thefrequencies of electrical signals to be transmitted, on the basis of theinformation, so as to obtain high transmission efficiency.

In the case where a plurality of power receivers exists within the rangein which communication with the power feeding device can be carried out,power can be transmitted only to a specific power receiver usingidentification information of the power receiver as described inEmbodiment 3.

Since identification information is found out and power feeding isperformed, a power receiver which is an intended object can be preciselymanaged, and an efficient service for a winner for a prize or the likeor a subscriber can be offered.

In addition, as described also in Embodiment 3, it is preferable to takemeasures for security, such as updating identification informationincluding specific information like personal information for each powerfeeding, deleting unnecessary identification information from a powerfeeding device after finishing a recognition step for power feeding, orencrypting communication when transmitting identification information.

This embodiment can be implemented in an appropriate combination withthe configurations described in the other embodiments.

This application is based on Japanese Patent Application serial no.2010-171575 filed with Japan Patent Office on Jul. 30, 2010, the entirecontents of which are hereby incorporated by reference.

1. A semiconductor device comprising: an antenna circuit; a rectifiercircuit; a demodulation circuit; a signal processing circuit portion; anoscillator circuit; a divider circuit; a switch; a mixer; and asecondary battery, wherein the antenna circuit is configured to receivean electromagnetic wave from a power feeding device and output anelectrical signal, wherein the rectifier circuit is configured torectify the electrical signal and generate a rectified signal, whereinthe demodulation circuit is configured to demodulate the rectifiedsignal and transmit a demodulated signal to the signal processingcircuit portion, wherein the signal processing circuit portion isconfigured to receive the demodulated signal and generate a transmissionsignal, wherein the oscillator circuit is configured to operate inresponse to the transmission signal and input a base carrier to thedivider circuit and the mixer via the switch, wherein the dividercircuit is configured to divide a frequency of the base carrier, therebygenerating signals having a plurality of frequencies which are lowerthan the frequency of the base carrier generated in the oscillatorcircuit, wherein the switch is configured to select one of the signalshaving the plurality of frequencies and transmit a selected signal tothe mixer, wherein the mixer is configured to mix the base carrier withthe selected signal, and is configured to transmit a mixed signal to theantenna circuit, wherein the secondary battery is configured to storefirst power transmitted from the power feeding device and supply secondpower to a power load portion, and wherein the switch is providedbetween the mixer and the divider circuit.
 2. The semiconductor deviceaccording to claim 1, wherein the power feeding device comprises: atransmission/reception circuit portion configured to transmit andreceive an electromagnetic wave; a signal processing circuit portionconfigured to process an electrical signal of the electromagnetic waveto be transmitted and received by the transmission/reception circuitportion of the power feeding device; and a power supply portionconfigured to supply power to be transmitted to a power receiver,wherein the signal processing circuit portion of the power feedingdevice has a position and resonant frequency detection function todetect a position and a resonant frequency of the power receiver, and apower transmission control function to control power to be transmittedto the power receiver.
 3. A wireless power feeding system comprising: apower feeding device; and a power receiver including a power receivingdevice portion, wherein the power feeding device comprises: atransmission/reception circuit portion configured to transmit andreceive an electromagnetic wave; a signal processing circuit portionconfigured to process an electrical signal of the electromagnetic waveto be transmitted and received by the transmission/reception circuitportion of the power feeding device; and a power supply portionconfigured to supply power to be transmitted to the power receiver,wherein the signal processing circuit portion has a position andresonant frequency detection function to detect a position and aresonant frequency of the power receiver, and a power transmissioncontrol function to control power to be transmitted to the powerreceiver, wherein the power receiving device portion comprises: atransmission/reception circuit portion configured to transmit andreceive an electromagnetic wave; a signal processing circuit portionconfigured to process an electrical signal of the electromagnetic waveto be transmitted and received by the transmission/reception circuitportion of the power receiving device portion; and a power storageportion including a secondary battery configured to store powertransmitted from the power feeding device and supply power to beconsumed by a power load portion, wherein the transmission/receptioncircuit portion of the power receiving device portion comprises anantenna circuit, a rectifier circuit, a mixer, a demodulation circuit,an oscillator circuit, a divider circuit, and a switch, wherein theswitch is provided between the mixer and the divider circuit, andwherein the signal processing circuit portion of the power receivingdevice portion has a power reception control function to control powerto be received from the power feeding device.
 4. The wireless powerfeeding system according to claim 3, wherein the transmission/receptioncircuit portion of the power feeding device comprises an antennacircuit, a rectifier circuit, a modulation circuit, a demodulationcircuit, an oscillator circuit, and a power supply circuit.
 5. Thewireless power feeding system according to claim 3, wherein the powerreceiver comprises a memory portion configured to store identificationinformation to be read by the signal processing circuit portion of thepower receiving device portion, and wherein the signal processingcircuit portion of the power feeding device has an identificationfunction to identify the identification information.
 6. A wireless powerfeeding system comprising: a power feeding device; and a power receiverincluding a power receiving device portion, wherein the power feedingdevice comprises: a transmission/reception circuit portion configured totransmit and receive an electromagnetic wave; a signal processingcircuit portion configured to process an electrical signal of theelectromagnetic wave to be transmitted and received by thetransmission/reception circuit portion of the power feeding device; anda power supply portion configured to supply power to be transmitted tothe power receiver, wherein the signal processing circuit portion of thepower feeding device has a position and resonant frequency detectionfunction to detect a position and a resonant frequency of the powerreceiver, and a power transmission control function to control power tobe transmitted to the power receiver, wherein the power receiving deviceportion comprises: a transmission/reception circuit portion configuredto transmit and receive an electromagnetic wave; a signal processingcircuit portion configured to process an electrical signal of theelectromagnetic wave to be transmitted and received by thetransmission/reception circuit portion of the power receiving deviceportion, a power storage portion including a secondary batteryconfigured to store power transmitted from the power feeding device andsupply power to be consumed by a power load portion; and a detectionportion configured to detect a voltage, a current, or a voltage and acurrent of the secondary battery, wherein the transmission/receptioncircuit portion of the power receiving device portion comprises anantenna circuit, a rectifier circuit, a mixer, a demodulation circuit,an oscillator circuit, a divider circuit, and a switch, wherein theswitch is provided between the mixer and the divider circuit, andwherein the signal processing circuit portion of the power receivingdevice portion has a power reception control function to control powerto be received from the power feeding device.
 7. The wireless powerfeeding system according to claim 6, wherein the transmission/receptioncircuit portion of the power feeding device comprises an antennacircuit, a rectifier circuit, a modulation circuit, a demodulationcircuit, an oscillator circuit, and a power supply circuit.
 8. Thewireless power feeding system according to claim 6, wherein the powerreceiver comprises a memory portion configured to store identificationinformation to be read by the signal processing circuit portion of thepower receiving device portion, and wherein the signal processingcircuit portion of the power feeding device has an identificationfunction to identify the identification information.
 9. A wireless powerfeeding method comprising: a first step of transmitting a position andresonant frequency detection signal using a plurality of sub-carriershaving different frequencies from a power receiver to a power feedingdevice and detecting a position and a resonant frequency of the powerreceiver with the power feeding device; a second step of adjusting afrequency of a power signal to be transmitted from the power feedingdevice on a basis of the position and the resonant frequency of thepower receiver and transmitting power from the power feeding device tothe power receiver; and a third step of storing the power transmittedfrom the power feeding device in a secondary battery of a power storageportion of the power receiver.
 10. The wireless power feeding methodaccording to claim 9, wherein the plurality of sub-carriers havingdifferent frequencies is adjusted by a switch provided between a dividercircuit and a mixer.
 11. The wireless power feeding method according toclaim 9, wherein the power receiver detects a voltage, a current, or avoltage and a current of the secondary battery and transmits a powerfeeding request signal or a power reception end signal to the powerfeeding device on a basis of the detection information.
 12. The wirelesspower feeding method according to claim 9, further comprising a step ofrecognizing identification information of the power receiver with thepower feeding device, before the first step.